Load-limiting device for auto substations



Aug. 11, 1925. 1,549,709

C. A. BUTCHER LOAD LIMITING DEVICE FOR AUTO SUBSTATIONS Filed Oct. 9, 1920 WITNESSES: INVENTOR Charles A. Bu rcfzer BY j AT'ToRNEY Patented Aug. l l 1925.

UNITED STATES 1,549,709 PATENT OFFICE.

CHARLES A. BUTCHER, F WILKINSBURG, PENNSYLVANIA, ASSIGNO'R TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

LOAD-LIMITING DEVICE non AUTO SUBSTATIONS.

Application filed October 9, 1920. Serial No. 415,769.

To all whom it may concern:

Be it known that I, CHARLES A. BUTCHER, a citizen of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Load- Limiting Devices for Auto Substations, of

. which the following is a specification.

My invention relates to automatic substations and particularly to load-limiting devices therefor.

-One object of my invention is to provide means for limiting the load that may be placed on a synchronous converter.

Another object of my invention is to provide means, of the above-indicated character, for gradually connecting the direct-current circuit of a machine to a load circuit after the machine has been disconnected therefrom because of an overload thereon.

A further object of my invention is to provide means of the above-indicated character that shall be simple, automatic and reliable in its operation.

Heretofore, large-heavy-grid-type re- ,sistors have been employed in automatic substations to limit the current traversing the circuit upon the occurrence of a heavy overload. The employment of a liquid rheostat controlled in accordance with the current traversing the circuit has been observed to give more satisfactory and more flexible operation because of the continuous adjustment possible therewith. Such a system embodying a liquid rheostat is, moreover, more flexible in direct-current Edison systems for restoring service after a short-circuit or heavy overload has served to effect the disconnection of the electrical generating apparatus from the system. In this system, the continuous adjustment of the value of the resistance in the liquid rheostat permits the gradual reconnection of the generating apparatus to. the system.

In view of the above conditions and observations, I provide two circuit interrupters connected in series with the conductors traversed by the current from the generating apparatus to the system or load circuit. The terminals of the liquid rheostat are respectively connected to the contact members of one of the interrupters that is adapted to be opened when traversed by a current exceeding a predetermined value. The reapparatus sistancebetween the terminals of the rheostat 1s varied by the adjustment of a plurahtyof movable electrodes through a rackand-pinion mechanism that is controlled by means of a motor that, in turn, is controlled 1n accordance with the value of current that traverses the circuit.

As the current tends to increase above a predetermined value, a relay, that is energized from a shunt in the circuit, so controls the motor as to effect an increase in the resistance in the liquid rheostat between, the terminals thereof to reduce the current traversing the circuit to a predetermined value. As the current decreases in the circuit below a predetermined value, the motor is so controlled as to decrease the resistance in the liquid rheostat between the terminals thereof. WVhen the resistance of the liquid rheostat is entirely eliminated, engagement is effected between two contact members that completes a circuit which energizes the closing means of the interrupter to short circuit the rheostat. The electrical is then directly connected, through the circuit interrupters, to the load circuit.

The single figure of the accompanying drawing is a diagrammatic view of an electrical circuit embodying my invention.

A source 1 of alternating electromotive force supplies energy to a translating device 2 that transforms the same into directcurrent energy which is supplied to a load circuit 3. The translating apparatus 2 is connected to the circuit 3 through a resistor or shunt 4 and a plurality of circuit interrupters 5 and 6. The contact members 7 and 8 of the interrupter 5 are respectively connected to the terminal members 9 and 10 of a liquid rheostat 11 comprising a 3% solution of sodium carbonate. The rheostat 11 further comprises a plurality of movable contact members, or electrodes, 12 and 13 that are controlled by a motor 14 through a rack-and-pinion mechanism 15. The motor 14. is controlled by a relay 16, the control winding 17 of which is energized from the shunt 4 in accordance with the current traversing the same.

The motor 14 comprises two field windof rotation thereof. The .energization of the windings 18 and 19 of the motor 14 it controlled'by means of the contact members 20 and 21, respectively, of the relay 16 which, when enga ed, are adapted to complete a circuit rom the conductor 22 throu h the corresponding winding 18 or 19 an the armature of the motor 14 to the conductor 23.

The actuation of the interrupter 6 15 controlled by a switch 24 that serves to complete a circuit from the conductor 22 through the actuating winding 25 of the interrupter 6 to actuate the same.

While the current that is supplied by the translatin device 2 to the circuit 3 is maintained be ow a predetermined value, the motor 14 is so operated as to diminish the value of the resistance between the terminal members 9 and 10 of the rheostat 11 by lowering the electrodes, 12 and 13. As the electrodes 12 and 13 are lowered by the rack-and-pinion mechanism 15, a contact member 26, that is supported by the rack member 15a, is gradually moved closer to a stationary contact member 27 with which it effects engagement immediately preceding the engagement of the terminal members 9 and 10 by the electrodes 12 and 13. Upon engagement of the contact members 26 and 27, a circuit is completed from the conductor 22, through the contact members 26 and 27 and the closing winding 28 of the interrupter 5, to the conductor 23, thereby energizing the winding 28 to close the mterrupter 5.

So long as the current that traverses the circuit comprising the conductors 22 and 23 is maintained below a predetermined value, a spring 29 of the relay 16 prevents the operation thereof to cause the motor to mcrease the resistance between the terminals 9 and 10 in the rheostat 11. Upon the occurrence of a heavy overload or shortcircuit, however, whereupon the current is caused to traverse the circuit including conductors 22 and 23 in excess of a predetermined value, the winding 30 of the interrupter 5 becomes sufliciently energized to open the same. Upon the opening of the interrupter 5, the resistance of the rheostat 11 is inserted in the circuit of the conductor 22. As the current that traverses the circuit of the conductor 22 continues to exceed a predetermined value, the winding 17 of the relay 16 becomes sufficiently energized to effect the engagement of the contact members 20, thereby causing the operation of the motor to increase the resistance of the rheostat 11 by raising the electrodes 12 and 13. As the additional resistance is inserted in the circuit of the conductor 22, the current that is permitted to traverse the same is decreased to a predetermined safe value.

A plurality of limit switches 31 and 32 is provided to prevent the energization of the motor, when the electrodes have reached their respective limits of travel.

In the Edison direct-current-systems in which a short-circuit or extremely heavy overload would effect the disconnection of the translating apparatus 2 from the circuit 3, the reconnection of the translating apparatus to the load circuit 3 would be established through the rheostat 11 with the entire resistance thereof effective. The resistance would then be gradually diminished until the apparatus 2 was able to supply the current demand of the circuit 3. Although the system is illustrated in a two conductor circuit, it is readil obvious that the same system may be app ied to a three conductor circuit by inserting a rheostat in each main conductor.

My invention is not limited to the arrangement or to the details of the apparatus as illustrated, as various modifications may be made therein within the s irit and scope of my invention as set fort in appended claims.

I claim as my invention:

1. In an electric circuit, the combination with a source of electromotive force, a variable load, and connecting means therebetween, of continuously adjustable resistance means, means for rendering the resistance means effective between the source and the load when the connecting means is opened, and means controlled by the value of current traversing the resistance means for controlling said current.

2. In an electric circuit, the combination with a source of electromotive force, a variable load, and connecting means therebetween, of liquid resistance means in circuit with the load comprising a movable electrode, means controlled by the current traversing the resistance means for controlling the position of the electrode, and means controlled by the position of the electrode for controlling the connecting means.

3. In an electric circuit, the combination with a source of electromotive force, a variable load, and connecting means therebetween, of means for opening the connecting means upon the occurrence of abnormal load conditions, continuously adjustable resistance means disposed between the terminals of the connecting means and rendered effective when the connecting means are opened, and means for controlling the resistance of said resistance means in accordance with the value of current trav ersing the same.

4. In an electric circuit, the combination with a source of electromotive force, a variable load, and connecting means therebetween, of a liquid rheostat connected in the circuit between the source of electromotive force and the load, means for rendering the rheostat effective upon the occurrence of abnormal load conditions, current-controlled means for controlling the rheostat in accordance with the current traversing the rheostat, and means for rendering the rheostat inefl'ective after the eflective resistance thereof is reduced to a predetermined value.

5. In an electric circuit, the combination with a source of electromotive force, a variable load and connecting means therebetween, of variable resistance means, means for inserting said resistance means in the circuit upon the occurrence of abnormal conditions and means responsive to the current thereafter traversing the circuit for so controlling the resistance means as to limit the current in the circuit to a predetermined.

value, and means for 'eli'minatin the resistor from the circuit when the e ective resistance is eliminated.

6. In an electric circuit, the combination with a source of electromotive force, a variable load and connecting means therebetween, of variable resistance means connect ed across the contact members of the connecting means, means for so opening the connecting means as to introduce the resistance means into the circuit, means for varying the resistance means to limit the value of current in the circuit and means for reclosing the connecting means when the resistance means has been so adjusted as to eliminate the resistance of saidmeans.

7. In an electric circuit, the combination with a source of electromotive force, a variable load and a plurality of circuit interrupters connected therebetween, of means for closing one interrupter, means for opening the second interrupter upon the occurrence of a heavy overload or short-circuit, a variable rheostat connected across the contact members of the second interrupter and permitted to become eflective when said interrupter opens, reversible means for controlling the adjustment of the rheostat,

means responsive to the circuit current for controlling the reversible means and means for reclosmg the rheostat shunting interrupter when the resistance of the rheostat has been eliminated.

8. In an electric system, the combination with a source of energy and a variable load, of a circuit interrupter connected between the source and the load, overload means for actuating the interrupter, a continuously variable resistor, means for connecting the resistor between the terminals of the interrupter, and means for radually varying the resistance value of tfie resistor to permit the source of energy to gradually assume the load.

9. In an electric system, the combination with a source of energy and a variable load, of a circuit interrupter connected between the source and the load, resistance means connected between the terminals of the circuit interrupter, and means responsive to the value of current traversing the resistance means for adually and continuously varying the e ectiveness thereof to permit the gradual assumption of the load by the source of energy.

10. In an electric system, the combination with a source of ener y and a variable load comprising a plura 'ty of incandescent lamps, of a circu1t interrupter connected between the source and the load, a gradually and continuously variable resistor, means for connecting the resistor in circuit between the source of energy and the load upon the occurrence of abnormal load conditions and means for gradually decreasing the efiective resistance of the variable resistor in accordance with the gradual increase of the resistance of the gradually heated incandescent lamps to permit the source of energy to gradually assume the load.

11. In an electric circuit, the combination with a source of energy, a variable load and connecting means therebetween, of a gradually variable resistor, means for including the resistor in circuit with said connecting means upon the occurrence of abnormal load conditions to permit a gradual assumption of the load by the source of energy and means for eliminating the resistor after a predetermined reduction in its resistance.

' 12. In an electric circuit, the combination with a synchronous converter, a variable load and connecting means therebetween, of a gradually variable resistor, means for including the resistor in said connecting means after the occurrence of abnormal conditions in the circuit to permit a gradual assumption of the load by the converter, and controllin means therefor comprising a motor an a relay energized in accordance with the circuit current for controlling the motor.

13. In an electric circuit, the combination with a synchronous converter a variable load and connecting means therebetween, of a gradually variable resistor, means for including the resistor in said connecting means after the occurrence of abnormal conditions in the circuit to permit a gradual assumption of the load b the converter, and controlling means there or comprising a relatively high-speed motor, suitable reduction earing driven by the motor to vary the ef- Iective resistance of the resistor and means responsive to the circuit current for controlling the motor,

In testimony whereof, I have hereunto subscribed my name this 6th day of October CHARLES A: BUTCHER, 

